James Webb Space Telescope

The James Webb Space Telescope (JWST) is a space telescope built to study the sky using infrared astronomy. It is the largest telescope in space. Its powerful instruments can see objects that are too old, too far away, or too faint for the Hubble Space Telescope. This helps scientists study many topics in astronomy and cosmology, such as the first stars, the formation of the first galaxies, and the air around potentially habitable exoplanets.

Webb's mirror is 2.7 times wider than Hubble's, yet it takes pictures with similar resolution. This is because it observes infrared light, which has longer wavelengths than the visible light that Hubble observes. For longer wavelengths, a telescope needs a larger surface to collect information in order to get the same level of detail.

Webb was launched on 25 December 2021 on an Ariane 5 rocket from Kourou, French Guiana. In January 2022, it reached its destination, an orbit around the Sun near the Sun–Earth L₂ Lagrange point, about 1.5 million kilometers (930,000 mi) from Earth. The telescope's first image was shared with the public on 11 July 2022.

The U.S. National Aeronautics and Space Administration (NASA) led Webb's design and development, working with the European Space Agency (ESA) and the Canadian Space Agency (CSA). The NASA Goddard Space Flight Center in Maryland managed the building of the telescope. The Space Telescope Science Institute in Baltimore, on the Homewood Campus of Johns Hopkins University, runs Webb. The main company that built the project was Northrop Grumman. The telescope is named after James E. Webb, who was the administrator of NASA from 1961 to 1968, during the Mercury, Gemini, and Apollo programs.

Features

Webb is about half the mass of the Hubble Space Telescope. Its 6.5-meter gold-coated primary mirror is made of 18 hexagonal mirrors and has a collecting area over six times larger than Hubble's. The gold coating helps it reflect infrared light. Webb is designed mainly for infrared astronomy. It can detect objects up to 100 times fainter than Hubble can and can see back to very early times in the history of the universe, near the Big Bang. Infrared light helps it study very distant objects, cold objects like planets, and light that passes through dust clouds. Ground telescopes must look through Earth's atmosphere, which blocks many infrared bands, so Webb is placed in space. To stay cold enough for its infrared work, it uses a large sunshield that blocks light and heat from the Sun, Earth, and Moon. Webb is kept at a steady temperature below 50 K.

Webb can also observe objects in the Solar System, including Mars, Jupiter, Saturn, Pluto, and comets and asteroids. It operates in a halo orbit around the Lagrange point L₂, which keeps it out of the shadow of Earth and the Moon. Its five-layer sunshield was folded to fit inside the Ariane 5 rocket. The spacecraft bus supports the telescope and provides power, communications, and other systems. Webb is not designed to be serviced in space the way Hubble was, though some features were added to make future remote servicing possible. Its instruments, including NIRCam, NIRSpec, MIRI, and FGS/NIRISS, were built by teams from several countries, including the European Space Agency and the Canadian Space Agency.

Comparison with other telescopes

The wish for a large infrared space telescope is decades old. In the United States, the Space Infrared Telescope Facility, later called the Spitzer Space Telescope, was planned while the Space Shuttle was being developed. Unlike telescopes on the ground, space observatories are not blocked by the air around Earth when they look at infrared light, which opened a "new sky" for astronomers.

Infrared telescopes must stay extremely cold, and the longer the wavelength of infrared light, the colder they must be. Otherwise, the device's own heat overwhelms its detectors and it becomes effectively blind. One method is to keep key instruments in a dewar filled with an icy substance, such as liquid helium, though the coolant slowly vaporizes and limits the instrument's life to a few months or a few years. Another method is to design the spacecraft to make near-infrared observations without coolant, as with the extended missions of the Spitzer Space Telescope and the Wide-field Infrared Survey Explorer, which kept working at reduced capacity after their coolant ran out. Hubble's Near Infrared Camera and Multi-Object Spectrometer (NICMOS) first used a block of nitrogen ice that ran out after a couple of years, but it was later replaced during the STS-109 servicing mission with a cryocooler that worked continuously. Webb is designed to cool itself without a dewar, using sunshields and radiators. Its delays and cost increases have been compared to those of its predecessor, the Hubble Space Telescope.

Development history

For a chronological guide, see Timeline of the James Webb Space Telescope.

Ideas for a follow-up to the Hubble Space Telescope began in the 1980s, and serious planning started in the early 1990s. In 1993, NASA carried out STS-61, the Space Shuttle mission that fixed Hubble's camera and corrected the spherical aberration in its primary mirror. A 1996 report then explored a larger, much colder telescope that could look back to the birth of the first galaxies, and NASA began planning for what became Webb. Dan Goldin, a NASA administrator, coined the phrase "faster, better, cheaper" and chose to break the barrier of a single mirror. Beryllium was chosen for the mirror because it is light, stiff, and keeps its shape in extreme cold. In 1999, NASA selected Lockheed Martin and TRW for preliminary studies. In 2002, the project was renamed after James E. Webb, NASA's second administrator. In 2003, NASA awarded TRW the main contract for the telescope, but later that year TRW was acquired by Northrop Grumman. Development was managed by NASA's Goddard Space Flight Center, with John C. Mather as project scientist. Northrop Grumman built the spacecraft, including the satellite bus and sunshield, while Ball Aerospace & Technologies built the Optical Telescope Element and the Integrated Science Instrument Module. Cost increases led to a re-plan in 2005 that delayed the launch by 22 months. Mirror segments were tested in cryogenic conditions at Marshall Space Flight Center, and the MIRI cryocooler was among the technologies that were checked. The mirror pieces were put together between 2015 and 2016. In 2018, the launch was delayed again after the sunshield tore during a practice deployment, and an independent review found 344 single-point failures, tasks that had to succeed. After final tests at Space Park in Redondo Beach, California, the telescope was shipped through the Panama Canal and arrived in French Guiana on 12 October 2021.

Costs grew over time. NASA's lifetime cost for the project was expected to be US$9.7 billion. In 2011, a House committee proposed canceling the project, but in November 2011 Congress reversed that plan and capped funding at US$8 billion. Senator Barbara Mikulski and the American Astronomical Society supported Webb. Gregory L. Robinson became program director in 2018 and raised the schedule efficiency from 50% to 95%. Several thousand people from 15 countries helped build the telescope, including partners such as Austria, Belgium, Canada, France, Germany, Italy, Spain, the United Kingdom, and the United States. In 2002, Sean O'Keefe chose to name the telescope after James E. Webb, who led NASA during the Mercury, Gemini, and Apollo programs. In 2015, concerns were raised about Webb's possible role in the lavender scare, when the U.S. government persecuted homosexuals in federal employment. Some people proposed other names, such as Harriet Tubman and Sally Ride. See also: James E. Webb § NASA, and James E. Webb § Legacy

Mission goals

The James Webb Space Telescope has four key goals. It will search for light from the first stars and galaxies that formed after the Big Bang, study galaxy formation and evolution, and learn about star formation and planet formation. It will also study planetary systems and the origins of life. Webb will mostly look at infrared light instead of visible and ultraviolet light, which is why it can do infrared astronomy so well. It will be able to sense wavelengths from 0.6 to 28 μm. It may also study the dimming of the star KIC 8462852, and it will be able to tell if an exoplanet has methane in its atmosphere, which could be a biosignature.

Webb orbits the Sun near the second Lagrange point (L₂) of the Sun–Earth system, about 1,500,000 km (930,000 mi) farther from the Sun than Earth is. Near L₂, the pull of Earth and the Sun lets the telescope orbit the Sun in the same time that Earth takes. It stays in a halo orbit around this point, which is tilted compared to the ecliptic. Small thruster firings, called station-keeping, keep it in place. The mission's total ∆v budget is 93 m/s. Staying close to Earth allows much faster data transfer. Randy Kimble compared this careful control to Sisyphus rolling a rock up a hill. Webb is the formal successor to the Hubble Space Telescope and is also a successor to the Spitzer Space Telescope. It will see much more distant and older stars and galaxies, partly because of cosmological redshift and because the universe is expanding. Infrared light passes through cosmic dust better than visible light. This lets scientists study places hidden from visible light, such as molecular clouds where stars form, circumstellar disks that form planets, and the cores of active galaxies. Cooler objects give off most of their energy as infrared light, following Planck's law. These include the interstellar medium, brown dwarfs, planets, comets, and Kuiper belt objects. Earlier missions such as Spitzer and the Wilkinson Microwave Anisotropy Probe (WMAP) showed how useful infrared observations are.

Ground support and operations

The Space Telescope Science Institute (STScI), in Baltimore, Maryland, on the Homewood Campus of Johns Hopkins University, was chosen in 2003 to run the science and operations center for Webb. It started with a budget of US$162.2 million to support operations through the first year after launch. STScI was to manage the telescope's science work and share its data with astronomers around the world. Data was to travel from Webb to the ground through the NASA Deep Space Network, then be processed at STScI and shared online. Anyone in the world can suggest observations. Each year, committees of astronomers peer review these suggestions and pick the projects for the next year. The researchers behind the chosen projects usually get one year of private access to their new observations, after which the data is available to download from the STScI online archive.

The telescope is designed to handle 458 gigabits of data per day, which is about 5.42 Mbps. Its data is digitized by a custom chip called the SIDECAR ASIC (Application Specific Integrated Circuit). Webb stores its science data temporarily on a solid-state drive with a capacity of 68 GB, which is expected to drop to 60 GB by the end of the 10-year mission. In May 2022, a tiny dust-sized micrometeoroid struck the C3 mirror segment, the fifth and largest strike since launch, and engineers had to compensate using a mirror actuator. A NASA report said that all of Webb's observing modes were confirmed ready for science use as of 10 July 2022. Micrometeoroids hit Webb about once or twice a month on average, but only the May 2022 strike caused noticeable damage. Mission staff then changed how Webb observes, avoiding pointing the mirror toward "micrometeoroid avoidance zones" at certain points along its orbit.

Launch and commissioning

Main article: Launch and commissioning of the James Webb Space Telescope

Main article: Ariane flight VA256

The launch, called Ariane flight VA256, took place on 25 December 2021 at 12:20 UTC. An Ariane 5 rocket lifted off from the Guiana Space Centre in French Guiana. The telescope was released from the rocket 27 minutes after launch and spent about a month moving into a Lissajous orbit around the L₂ Lagrange point. It reached L₂ on 24 January 2022, after three planned course corrections. Space.com called the launch "flawless." Because an L₂ orbit is unstable, the telescope uses fuel to stay in place, a process known as station-keeping.

Over about 13 days, the telescope unfolded its solar array, antenna, sunshield, and mirrors. Nearly all of these steps were commanded from the Space Telescope Science Institute in Baltimore, Maryland. The mirror wings had been folded to fit inside the fairing of the rocket, and they were unfolded to complete the structure. A final course correction on 24 January 2022 placed Webb in its planned halo orbit around the Sun–Earth L₂ point. Mirror alignment began on 12 January 2022 and took about 10 days. The telescope uses 132 actuator motors that move in steps of about 10 nanometer increments. Using the NIRCam instrument, the team aimed at a star in Ursa Major and used a technique called phase retrieval to line up the 18 mirror segments. The mirrors must be aligned to within 50 nanometers, less than one wavelength of the light the telescope detects. NIRCam detected the telescope's first photons on 3 February 2022. Phase 1 of alignment was completed on 18 February 2022, and phases 2 and 3 were completed a week later.

Allocation of observation time

Webb observing time is shared through several programs. The GTO program gives guaranteed time to scientists who developed hardware and software for the telescope. The GO program lets all astronomers apply and makes up most of the observing time. Its programs are chosen through peer review by a Time Allocation Committee (TAC), similar to the process used for the Hubble Space Telescope. The DDT program is used for time-critical observations.

In November 2017, the Space Telescope Science Institute chose 13 Early Release Science programs through a competitive proposal process. These observations, called Early Release Observations (ERO), were to be made during the first five months of Webb science after commissioning. The programs were given 460 hours of observing time and cover topics including the Solar System, exoplanets, stars and star formation, nearby and distant galaxies, gravitational lenses, and quasars. For Cycle 1, 6,000 hours were available, and 1,173 proposals requesting 24,500 hours were submitted. In Cycle 4, the telescope received 2,377 proposals requesting 78,000 hours, nine times the amount available.

Scientific results

The JWST finished its testing period and began full science work on 11 July 2022. Most experiment data is kept private for one year for the scientists running that experiment, and then the raw data is released to the public. U.S. President Joe Biden revealed the first image, Webb's First Deep Field, on 11 July 2022. The first full-color images were released on 12 July 2022. Other early images included the young star-forming Carina Nebula and Stephan's Quintet, a group of five galaxies. JWST observations greatly advanced understanding of exoplanets, the first billion years of the universe, and other objects in space.

Within two weeks of the first images, scientists described very bright galaxies that existed far earlier than previously known. In May 2024, the JWST found the most distant known galaxy, JADES-GS-z14-0, seen just 290 million years after the Big Bang. Later studies of very early black holes and new discoveries about exoplanet clouds and atmospheres continued to add to what scientists know.